Double clutch transmissions with various configurations have been known for a long time. Apart from special designs, a common feature of all double clutch transmissions is that they have two input shafts, the first of which is formed as a shorter, hollow shaft and the second is longer and is arranged coaxially inside the first input shaft. The two input shafts can be connected to the drive shaft of a drive motor, in each case by way of an associated friction clutch of a double clutch arrangement.
Different versions of double clutch transmissions differ from one another essentially in the number and arrangement of countershafts and in the disposition of the output shafts. Further differing features of double clutch transmissions consist in the type and number of driving connections between the transmission shafts, which can be in the form of input constants, output constants, or shiftable gear ratio steps.
For example, DE 35 46 454 C2 describes a double clutch transmission with a first input shaft in the form of a hollow shaft, a longer, second input shaft arranged coaxially inside the first input shaft, and a countershaft arranged axis-parallel to the two input shafts. At the same time the countershaft forms the output shaft of the double clutch transmission and for that purpose has at its end on the motor side a bevel pinion for driving a bevel gear of an axle differential. By way of associated shiftable gear wheel sets whose fixed wheels are arranged respectively on one of the input shafts, the two input shafts can be selectively connected to the output or countershaft; the first input shaft via the gear wheel set of the even gears (G2, G4) and the second input shaft via the gear wheel set of the uneven gears (G1, G3, G5) and the reverse gear (R). A special feature is that the known double clutch transmission comprises a shiftable clutch for coupling the two input shafts, whereby during starting off the two friction clutches can at the same time be used as starting clutches, so avoiding unacceptably severe heating of a single friction clutch.
In contrast, DE 41 23 493 C2 describes a double clutch transmission with a first input shaft formed as a hollow shaft, a longer, second input shaft arranged coaxially inside the first input shaft, and a countershaft arranged axis-parallel to the two input shafts, in which the output shaft is formed by a further transmission shaft arranged colinearly, i.e. coaxially and axially adjacent to the two input shafts. Whereas the first input shaft is in driving connection with the countershaft via an input constant, the second input shaft can be connected selectively to the countershaft by way of two shiftable input gear ratio steps whose fixed wheels are arranged on the second input shaft. On the output side, the countershaft can be selectively connected, via three shiftable output gear steps, to the output shaft which, to engage a direct gear, can also be coupled directly to the second input shaft.
A further double clutch transmission with a first input shaft made as a hollow shaft and a longer, second input shaft arranged coaxially inside the first input shaft is known from DE 101 53 014 A1. This double clutch transmission has two countershafts arranged parallel to the two input shafts, which together with the two input shafts are arranged in a V-shape and are in connection with a common drive output element, in each case by way of a fixed output wheel. To engage the uneven gears (G1, G3, G5) the second input shaft can be connected selectively, via shiftable gearsets, to the first countershaft and to the second countershaft. To engage the even gears (G2, G4, G6) and the reverse gear (R), the first input shaft can be connected selectively, via shiftable gearsets, to the first and to the second countershaft. The fixed wheels of the gearsets are respectively arranged on the associated input shafts.
In transmissions of countershaft design and also in double clutch transmissions, the radial distance between the input shafts and the countershafts can deviate from the ideal value by an amount on the order of a few tenths of a millimeter. Moreover, deflection of the load-transmitting input shafts and countershafts under load results in further deviations from the ideal radial distance. At the gear wheels of the non-load-transmitting input constants and of the shiftable gear steps such deviations can result in jamming and consequently to reduced transmission efficiency and increased wear. Whereas in the case of the shiftable gears, jamming can usually be avoided by virtue of a greater axial play of the radial bearings by which the loose wheels are mounted to rotate on the transmission shaft concerned, until now no suitable measure for this has been known for fixed wheels of the transmission arranged in a rotationally fixed manner on an input shaft.